[ M ] 
vulcanic diftri61s of Auvergne and Velay, as well as thofe 
of the Venetian ftate, afford proofs enough of the truth 
of this opinion ; but I fliall confine myfelf at prefent to 
the latter, and particularly to the phaenomena of this 
kind, which I obferved in the Vicentine and Veronefe 
mountains, and which, if 1 miflake not, will appear de- 
cifive in the queftion before us. 
Thefe mountains occupy the lower fkirts of the Alps^on 
the north fide of Lombardy, and are partly vulcanic, and 
partly of limeftone. They form fub-divifions, or lateral 
branches of the great chain of the Alps, from which they 
diverge, nearly at right angles, and extend in a fouthern 
dire6lion, and parallel with each other, towards the plain. 
Some of thefe branches are intirely of Umeftone, without 
any lava ; others are compofed of a mixture of both ; and 
others again are exclufively vulcanic. I have rode from the 
point of one of them near Montebello, in the Veronefe 
territory, to Bolca, always upon lava^ for the diftance of 
near twenty miles. It is along this branch, by the fide 
of the valley leading to Bolca, and about four or five miles 
fhort of it, that the caufeway of San Giovanni Illarione 
before defcribed is fituated. The whole folid mafs of 
this branch, as far as I could obferve, is almofi: intirely 
compofed of lava^ which, . about the fkirts and furface 
particularly, is of various kinds. Among others very cu- 
rious, I remarked fome, at the foot of the cafUe hill near 
Montebello, concreted in different maffes, which, by their 
extreme hardnefs, heterogeneous texture and colour, very 
much refemble an ordinary fort of porphyry. But I faw 
no 
